Bought a four pack, three connected no problem. Fourth one would go into pairing mode but would not connect. They sent me a replacement bulb, came today pulled it out the box and screwed into the fixture. It will not enter pairing mode. When installed into the light it powers on in red but with not flash. I have tried every light fixture in my home. I unscrewed it and laid on the kitchen counter, going to let it sit for 30 mins and try it again, If it still won’t connect screw-it, time to find a new product.
Did you do the 3x “short-delay on-off” sequence to put it back in paring mode? Usually fixes the issue.
Chances that you got a defective replacement after a new one is considered defective are pretty slim. I would bet in an environmental issue there - signal issue at this location for example.